netdev - Re: [PATCH v4 02/15] x86/msr: Move rdtsc{,

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Message-ID: <aBR8EoYkxaFHwZN2@gmail.com>
Date: Fri, 2 May 2025 10:02:26 +0200
From: Ingo Molnar <mingo@...nel.org>
To: "Xin Li (Intel)" <xin@...or.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
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Subject: Re: [PATCH v4 02/15] x86/msr: Move rdtsc{,_ordered}() to <asm/tsc.h>


* Xin Li (Intel) <xin@...or.com> wrote:

> index 94408a784c8e..13335a130edf 100644
> --- a/arch/x86/include/asm/tsc.h
> +++ b/arch/x86/include/asm/tsc.h
> @@ -7,7 +7,81 @@
>  
>  #include <asm/cpufeature.h>
>  #include <asm/processor.h>
> -#include <asm/msr.h>
> +
> +/*
> + * both i386 and x86_64 returns 64-bit value in edx:eax, but gcc's "A"
> + * constraint has different meanings. For i386, "A" means exactly
> + * edx:eax, while for x86_64 it doesn't mean rdx:rax or edx:eax. Instead,
> + * it means rax *or* rdx.
> + */
> +#ifdef CONFIG_X86_64
> +/* Using 64-bit values saves one instruction clearing the high half of low */
> +#define DECLARE_ARGS(val, low, high)	unsigned long low, high
> +#define EAX_EDX_VAL(val, low, high)	((low) | (high) << 32)
> +#define EAX_EDX_RET(val, low, high)	"=a" (low), "=d" (high)
> +#else
> +#define DECLARE_ARGS(val, low, high)	u64 val
> +#define EAX_EDX_VAL(val, low, high)	(val)
> +#define EAX_EDX_RET(val, low, high)	"=A" (val)
> +#endif

Meh, this patch creates a duplicate copy of DECLARE_ARGS() et al in 
<asm/tsc.h> now:

 arch/x86/include/asm/msr.h:#define DECLARE_ARGS(val, low, high) unsigned long low, high
 arch/x86/include/asm/msr.h:#define DECLARE_ARGS(val, low, high) u64 val
 arch/x86/include/asm/msr.h:     DECLARE_ARGS(val, low, high);
 arch/x86/include/asm/msr.h:     DECLARE_ARGS(val, low, high);
 arch/x86/include/asm/msr.h:     DECLARE_ARGS(val, low, high);
 arch/x86/include/asm/tsc.h:#define DECLARE_ARGS(val, low, high) unsigned long low, high
 arch/x86/include/asm/tsc.h:#define DECLARE_ARGS(val, low, high) u64 val
 arch/x86/include/asm/tsc.h:     DECLARE_ARGS(val, low, high);
 arch/x86/include/asm/tsc.h:     DECLARE_ARGS(val, low, high);
 arch/x86/include/asm/tsc.h:#undef DECLARE_ARGS

Which was both an undeclared change, bloats the code, causes various 
problems, and is totally unnecessary to boot.

Please don't do that ...

Thanks,

	Ingo